| Statement | Response | Comment |
| Some substances give out radiation all the time, whatever is done to them. They are said to be . . . | radioactive. | Radioactivity is a random process - we cannot predict when a given atom will emit radiation. |
| There are three types of radiation emitted by radioactive sources . . . | alpha, beta and gamma. | Other types of particle can be emitted but we need not concern ourselves with them at the moment. |
| Alpha radiation is easily absorbed by . . . | thin sheets of paper or a few cm of air. | They are easily stopped by your skin or clothing. |
| Alpha particles are actually composed of . . . | helium nuclei. | 2 protons plus 2 neutrons. |
| Beta particles are actually . . . | electrons. | They are emitted from the nucleus but they are the same as those in orbit round it. |
| Gamma rays are . . . | a form of electromagnetic radiation. | It has very short wavelength and travels at the same speed as light. |
| Beta particles travel at nearly the speed of light but are mostly absorbed by . . . | a few mm of metal. | Aluminium will absorb them but lead is better. |
| Gamma rays are very penetrating and can only be absorbed by . . . | many cm of lead or metres of concrete. | They do not interact very strongly with matter so are difficult to stop. |
| There are radioactive substances all around us, particularly in . . . | the ground, air, in building materials and food. It is known as background radiation. | We grow up in a radioactive environment - perhaps that is what drives evolution? |
| Radiation which reaches us from space is known as . . . | cosmic rays. | They are produced in supernova explosions. |
| When radiation from radioactive materials collides with neutral atoms or molecules, they may become . . . | ionised (charged) | The term 'ionising radiation' is often used. |
| When radiation ionises molecules in living cells it can cause damage, including . . . | cancer. | The larger the dose, the greater the risk. |
| Higher doses of radiation are used to . . . | kill cancer cells and harmful micro-organisms. | Sterilisation of surgical instruments. |
| As radiation passes through a material it can be . . . | absorbed. | The greater the thickness, the more is absorbed. |
| The absorption of radiation can be used to . . . | monitor or control the thickness of materials. | For example, paper or aluminium 'bacofoil' |
| When sources of radiation are outside the body, which types are most dangerous? | Beta and gamma | because they can penetrate the skin to reach the cells of organs and may be absorbed by them. |
| Outside the body, which type of radiation is least dangerous? | Alpha | because it cannot penetrate the outer layers of clothing or skin. |
| Workers who are at risk from radiation wear a film badge. Why? | If the film turns black when developed, they have been exposed to too much radiation. | Different layers of absorbers on top of the film can tell us what type of radiation has caused the exposure. |
| When sources of radiation are inside the body, which are most dangerous? | Alpha | because it is strongly absorbed by cells. |
| Inside the body which types of radiation are least dangerous? | Beta and gamma | because they can escape the body and are less likely to be absorbed. |
| The half life of a radioactive substance is . . . | the time taken for half the number of radioactive atoms in a sample to decay. | This is an average time - decay is a random process. |
| The half life of a substance can also be . . . | the time taken for the count rate to halve. | The rate of decay is proportional to the number of radioactive atoms in a sample. |
| The nucleus which emits radiation is referred to as a parent. What is its decay product called? | A daughter | That's politically correct at least! |
| Radioactive isotopes are used as tracers. What is a tracer? | A substance which is introduced into a person or a water supply to monitor the movement of blood or water through the system. | Beta and gamma radiation are usually used for this. |
| What type of radiation would be most suitable for use as a biological tracer in a patient? | Gamma | because it is not easily absorbed by the cells and will cause little damage. |
| Atoms have a small nucleus made up of . . . | protons and neutrons | Protons are positively charged. Neutrons have zero charge |
| Electrons are negatively charged and are usually found . . . | moving around the nucleus | They are NOT like planets going around the Sun ! |
| What task did Ernest Rutherford set to his students, Geiger and Marsden? | To fire alpha particles at a sheet of gold foil. | Why gold foil ?
(The foil can be made very thin so that the alpha particles only made single collisions with gold atoms.) |
| What did Rutherford's experiment prove? | The nucleus is tiny, very massive and positively charged. | JJThomson thought it was like a plum pudding - how daft ! |
| In Rutherford's experiment, what were the main observations? | Most of the alpha particles missed the nucleus, but a few bounced straight back. | Like a cannonball reflecting from tissue paper ! |
| All atoms of the same element have the same number of . . . | Protons | I don't care about the electrons !! |
| In a neutral atom, there must be the same number of . . . | Protons and electrons | Now I care ! |
| Isotopes are . . . | atoms of the same element which have different numbers of neutrons in the nucleus. | You can forget the electrons now. |
| The total number of protons and neutrons in an atom is called its . . . | mass or nucleon number. | See - no electrons even mentioned. |
| Radioactivity occurs because of . . . | changes in the nuclei of atoms. | Electrons are NOT involved in nuclear Physics. |
| Radioactive isotopes are also called . . . | radioisotopes or radionuclides | They have UNSTABLE nuclei which split up and emit radiation. |
| When an unstable nucleus decays it . . . | becomes a different nucleus with a different number of protons and neutrons. | The electrons just hang around until something better comes along. |
| When a gamma ray is emitted by a radioactive nucleus . . . | there is no change to the structure of the nucleus - it just cools down a bit. | Gamma rays have no mass or charge - they just carry energy away from the nucleus. |
| Alpha decay results in the nucleus losing . . . | 2 protons and 2 neutrons | An alpha particle is just a helium nucleus - they exist inside heavy nuclei in clusters. |
| A beta decay occurs when . . . | a neutron changes into a proton - it emits an electron which takes away negative charge. | Bit like a sex change ! |
| The older a radioactive material . . . | the less radiation it emits. | Can be used to date materials and rocks. |
| Nuclear reactors use a process called . . . | nuclear fission. | A heavy nucleus (uranium) absorbs a slow neutron and splits ( fissions) into two lighter nuclei plus neutrons. |
| The products of nuclear fission are themselves radioactive. This causes problems because . . . | they are hard to dispose of properly. | They must be stored carefully for hundreds of years. |
| The energy released during nuclear fission is . . . | very large compared with chemical reactions. | Those involving electrons ! |
| Uranium isotopes which have a long half life, decay by a series of short-lived isotopes to produce . . . | stable isotopes of lead. | Lead has more stable isotopes than any other element. |
| The age of a rock can be found by comparing . . . | the relative proportions of uranium and lead in the rock. | Igneous rock can be dated this way because its initial composition is fixed when it solidifies from lava. After this radioactive minerals start to decay - the clock is ticking. |
| The radioisotope potassium-40 can be used to date igneous rocks because . . . | its stable decay product argon is unable to escape from the rock. | Apply the idea of half life to the ratio of what remains to what was there initially. |
| If an igneous rock is found to contain 3 atoms of argon for every 1 of potassium-40, how old is the rock? | Two half lives | because only 1/4 of the original potassium remains. |
| Carbon-14 is a radioactive isotope of carbon-12. How is it used? | To date organic remains. | Living things breathe in C14 while alive, but after death the C14 decays to Nitrogen. |
| How much of radioactive material X remains after 3 half lives | 1/8 | 1/2 x 1/2 x 1/2 = 1/8 |
